This invention concerns improvements made to equipment for manufacturing hollow plastic bottles or the like from preforms, equipped with means for swinging the preforms.
In conventional machines for the manufacture of such hollow objects by blowing or stretching-blowing, at least the following components are provided; a thermal processing station in which the preforms are heated to a temperature such that they may be molded by blowing or stretching/blowing; a preform blowing station having molds shaped like the hollow parts to be produced; and conveyors which bring the preforms to the thermal processing station and transfer them to the blowing station.
In a machine of this type, the preforms are conveyed to the thermal processing station in the vertical position, the open neck or mouth of the preforms being turned upward. The heating of the preform in the neck-up position does not lead to satisfactory thermal processing, however. Indeed, since heat has a tendency to rise, the neck positioned on top is also heated, and therefore tends to become deformed and to lose the final configuration imparted to it during the manufacture of the preform.
The conventional solution to this problem consists in heating the preform with the neck on the bottom, in order to avoid the above-mentioned deformation of the neck. It is necessary, therefore, to provide a reversing device which makes it possible to move the preform from the neck-up to the neck-down position before heating, then to bring it back to the neck-up position for the rest of the process for the manufacture of a completed hollow bottle.
One example of a known reversing device is described and illustrated in FIGS. 4 and 5 of French Patent No. 2,479,077. Each preform is held by a support mounted to pivot by means of a pin on a frame. The reversal of the preform support is accomplished by a toothed sector driven by a cam, which meshes with a toothed pinion which rotates as one piece with the pin of the support.
This device, although working satisfactorily, is difficult to adjust (in particular to establish parallelism of the teeth of the toothed sector and of the pinion) and burdensome to manufacture. In addition, the machine has a relatively complex structure.